Effect of increased soft tissue thickness on bone density and microstructure measurements using the 2nd generation...

Bone density and microarchitecture measurements from high-resolution peripheral computed tomography (HR-pQCT) are increasingly being used to predict fracture risk and to gain insight into the pathophysiology of skeletal fragility. Using the first-generation HR-pQCT scanner, we previously showed that extraosseous soft tissue can impact HR-pQCT measurements. Yet similar data is not available for the second-generation scanner. Thus, we aimed to determine the impact of increased soft tissue on bone density, microarchitecture and strength measurements acquired using the second-generation HR-pQCT scanner. We performed HR-pQCT scans on a hydroxyapatite phantom and in human volunteers (n = 12) with no soft tissue covering, and with a thin (0.5 cm) and thick (1 cm) layer of soft tissue surrounding the phantom or limb. We found that density values of the phantom were minimally affected by the thin layer of soft tissue. In contrast, with the thick (1 cm) layer of soft-tissue, bone density was significantly lower than baseline (no bolus), with greater deficits as the density of the rod increased (-1% to -3.6%, p < 0.01 for all). In human volunteers, soft tissue layering influenced measures of both cortical and trabecular microarchitecture at the distal tibia and radius, with larger differences observed in trabecular versus cortical measures and at the tibia compared to the radius. For example, at the tibia, Tt.BMD was lower than the baseline scan under both soft tissue layering conditions (thin: -1.3%, p < 0.001; thick: -2.4%, p = 0.003), while at the radius Tt.BMD was only significantly lower for the thick layer (-1.2%, p = 0.004). Ct.BMD followed a similar pattern, with slightly greater magnitude of BMD decline with increased soft tissue (thin: -1.5%, p < 0.001, thick -2.8%, p < 0.001 at the tibia) compared to Tt.BMD. Altogether our results indicate that HR-pQCT measurements at both the metaphyseal and diaphyseal sites must be interpreted carefully when comparing subjects with varying body composition, or when assessing longitudinal changes in individuals who experience marked changes in weight and/or body composition as true differences to these measures may be more or less extreme than they appear.